ASoC: rsnd: DMA cleanup for flexible SSI/SRC selection

Current R-Car sound SSI/SRC/DVC selection has feature limit.
(It is assuming that SSI/SRC are using same index number)

So that enabling SSI/SRC flexible selection,
this patch modifies DMA settings.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@linaro.org>